DESCRIPTION: (Applicant's Abstract) Syringe exchange programs have become standard approaches to HIV prevention for injection drug users in many communities in the US. Early research on needle exchange program reported strong protective effects against injection risk behavior and infection with blood-borne viruses 1-4. Several recent studies, however, have reported negative or null effects of the programs 5-7. Our analysis of the RAVEN Study (an epidemiologic study of the Seattle Needle Exchange) did not show a protective effect of the program against hepatitis B virus (HBV) or hepatitis C virus (HCV) infection 8. In fact, incidence was highest among users of the exchange. In this continuation of RAVEN, we propose to further study factors that may be working against the needle exchange in prevention of HIV and other blood-borne viruses. The specific aims of the continuation are: 1. Examine time-related influences on the association between needle exchange and HIV risk. We will follow a fixed cohort of 850 RAVEN participants for an additional two years, and, using the method of birth cohort' analysis, study whether the apparent effect of the exchange has been influenced by changes in the prevalence of risk behavior, migration of low-risk IDUs out of the needle exchange, or by the waning of a cohort-effect that led to more substantial effects in early years of exchange operations. 2. Systematically assess linkages to high-prevalence populations as a risk factor for HIV infection among Seattle area injectors. We will monitor targeted IDU groups who inject in the company of or have sexual contact with members of high HIV-prevalence populations to detect changes in HIV infection. 3. Evaluate the impact of needle exchange operations characteristics on factors associated with the risk of blood borne viruses. The needle exchange environment and operations will be studied in detail to understand whether other factors at work in the vicinity of the exchange, or service-delivery aspects of the program impede the ability of some IDUs to benefit from needle exchange. The significance of this research will be to understand more fully what is accomplished by needle exchange, and what may be needed to achieve better results.